Electronic article surveillance system are well known and are used for purposes of inventory control and to prevent theft and unauthorized removal of articles from a controlled area. Typically, in such systems, a system transmitter and a system receiver are used to establish a surveillance zone which must be traversed by any articles being removed from the controlled area.
An EAS tag is affixed to each article and includes a marker or sensor adapted to interact with a signal that is transmitted by the system transmitter into the surveillance zone. This interaction causes a further signal to be established in the surveillance zone which further signal is received by the system receiver. Accordingly, upon movement of a tagged article through the surveillance zone, a signal will be received by the system receiver, identifying the unauthorized presence of the tagged article in the zone.
Certain types of EAS tags have been designed to be reusable and, thus, include releasable attachment devices for affixing the tags to the articles. Such attachment devices are further designed to be releasable by authorized personnel only so that unauthorized removal of a tag from its article is avoided. To this end, many attachment devices are made releasable only through the use of an associated special tool or detaching mechanism. Examples of detaching units which may be employed to separate reusable, removable EAS tags from articles of merchandise are disclosed in U.S. Pat. Nos. 5,426,419; 5,528,914; and 5,535,606. (The disclosures of these three patents are incorporated herein by reference.) The detaching units disclosed in these patents are designed to operate upon a two-part "hard" EAS tag, formed of a molded plastic enclosure portion which houses EAS marker elements, and a tack or pin member which is inserted through an article of merchandise to be protected (such as an item of clothing) and then also inserted into the enclosure portion of the tag. The enclosure portion of the tag includes a clamp for securely holding the pin in the enclosure portion.
The detaching unit is operated to insert a probe into the enclosure portion of the tag to release the clamp. The pin may then be released from the enclosure portion of the tag, and the tag removed from the article of merchandise. A detaching device which embodies teachings of the '419, '914 and '606 patents is sold by the assignee of this patent application, Sensormatic Electronics Corporation, as Model No. MK200.
One problem that must be faced in connection with removable EAS tags is the possibility of unauthorized removal of the tag from the article of merchandise for the purpose of defeating the EAS system. To prevent unauthorized removal of hard tags, it has been known (as in U.S. Pat. No. 5,005,125, for example) to provide the tags with an alarm arrangement which generates an audible alarm signal upon detection of an attempt to tamper with the enclosure portion of the tag. It is also known to secure detaching units with a lock-and-key arrangement, so that only those having possession of the required key are able to use the detaching units. However, if a store employee with access to the key chooses to participate in an attempt to defeat the EAS system, then unauthorized use of the detaching unit to remove the hard tags from the merchandise may take place.